Air-cooled 14-cylinder double-row radial engine.

In the first decade of the 20th century Anzani developed his upright 3-cylinder 'W' type motorcycle engine, which powered Bleriot's successful Channel crossing flight of 1909, into a three-cylinder symmetric or 'Y' radial, and from that to a 6-cylinder double-row radial engine.

Although both types were powered by the widely used Pratt & Whitney R-2800 Double Wasp eighteen-cylinder, double-row radial engine, they were completely different and separate designs - the Martin bomber originated in 1939, with roughly twice as many Marauders (nearly 5,300) produced in comparison to the Douglas design.